1. Field of the Invention
The invention relates in general to a compensation apparatus for image scan, and more particularly, to an apparatus for compensating the optical path deviation caused by vibration of an optical scanner.
2. Description of the Related Art
As use has increased and with breakthroughs in the technology of photosensitive devices, the resolution of optical scanners has steadily increased from the early 200 dots per inch (dpi) for a black-and-white scan and gray scale scan to 300 dpi, 600 dpi, 1000 dpi, and now 2000 dpi and 4000 dpi for a color scan today. As the resolution is continuously enhanced, the scanner becomes more and more sensitive to the machine's vibration.
In a typical optical scanner, after first being projected onto an object to be scanned and then reflected by the object to a series of planar mirrors, a light source is subsequently projected onto a charge coupled device (CCD) to be converted into a digital signal to be read. When the driving system operates to drive the lens or the charge coupled device, vibration occurs that affects the scanning quality. In FIG. 1, the optical path deviation caused by the vibration of the scanner is shown. While the optical scanner is performing a scan, the driving system 109 drives the optical system 111 (that is, the planar compound mirror 104, the lens 106 and the photosensitive device 110) along the scanning direction 107. As the optical system 111 moves a small distance, the photosensitive apparatus 110 scans and detects the object 100 once. The optical path is from the light source (not shown), the object 100, the planar compound mirror 104, the lens 106 and the photosensitive apparatus 110. During the scan, the driving system generates a vibration to the optical system 111, so that an optical path deviation N′N is generated. A chromatic aberration occurs to the scanned image, such that the image quality is deteriorated. The vibration of the optical system and the optical path deviation N′N may occur along the x-axis, y-axis and z-axis. FIG. 1 only illustrates the vibration along the y-axis to describe the optical path deviation along z-axis as an example.